I have a 1991 Cadillac Deville with a 4.9L. When I have the car in gear and am accelerating, there is a rattling noise coming from the engine bay area. It happens all of the time and is most noticeable when driving past a wall with the windows down. Lower RPMs make it louder and at higher RPMs when the engine is under strain, the noise is almost nonexistent. Any suggestions?

Maybe a loose heat shield in the engine area

Update: while driving today with the A/C on, the car lost power steering and displayed the battery and oil lights. Engine was still running so I turned it off. I checked under the hood, turned off HVAC, and restarted. Usual rattling sound was still present but was able to drive it home.

I drove it a second time after that and it appeared to drive like usual. I had the HVAC off the entire time. As soon as I turned on the A/C at the end of my trip, the car did the same thing- no power steering, battery and oil lights and engine still running. Turned HVAC off and resumed like normal. Rattling still present.